1. Field of the Invention
The present invention relates generally to panel drip testing used to evaluate the effectiveness of coating cleaners in removing coating from a coated surface and, more particularly, to a method and apparatus for quantitatively evaluating the results of panel drip tests.
2. Description of Related Art
Blends of solvents are typically used to clean-up coating residues in many coating applications. One such use of these solvent blends is the purging or cleaning of coating residue in automated coating application equipment between color changes. The performance of these solvent blends is crucial to ensure proper coating application and maintenance of the equipment.
Laboratory testing methods have been used in the purge solvent industry to compare one blend of solvents to another. The most common test to screen or evaluate solvent blends is collectively known in the industry as the “drip” test. In this test, a specified film thickness of coating (i.e., coating) is applied to a clean glass test plate. The coated glass test plate is allowed to air dry for a specified number of minutes and then placed in a rack at a fixed angle. The solvent blend to be tested is then dripped onto the film at a fixed rate and the coated glass test plate is removed after a predefined number of drips have hit the surface of the glass test plate. Alternatively, the drip test may be discontinued after a set or defined portion of the glass test plate has been cleaned by the solvent blend. The glass test plate is then compared to a control solvent applied using the same parameters. A typical setup for such drip tests would involve a glass test plate coated with 1.5 mil of coating dried for 2 minutes, and then applying a solvent at a rate of 1 drop per second until 10 drops have been applied.
The solvent dissolves away a portion of the coating from the coated surface. When evaluating several solvent blends to determine the optimum product, the glass test plates treated with the different solvent blends are compared visually and the rough area where the solvent cleaned the glass test plate is compared. Many solvent blends are easily visually differentiated through this test, allowing the experimenter to quickly discern the better purge solvent product. Some solvent blends, however, are not so easily visually differentiated and there are no quantitative measures currently available in the art to differentiate between various solvent blends. Thus, the relative effectiveness of solvent blends tested using a drip test is often dependent on the experimenter's subjective interpretation.
Methods and devices are known in the art for evaluating the surface quality such as roughness or scratches and other parameters of materials and substrates using ultrasound, lasers, and the like.
Methods and devices are specifically known in the art for detecting faults in and evaluating the quality of flat glass panels using, for example, infrared sensors, and/or video cameras to monitor an illuminating device passing below the glass. The change of intensity of the two video signals is then used to evaluate the optical quality of the glass panel and locate faults within the glass panel.
Even though such methods and devices are known in the art for detecting and evaluating the surface quality and other parameters of materials and substrates, these methods and devices are not generally applicable to evaluating panel drip tests. In view of the foregoing, a need exists in the field of panel drip tests for a method of objectively evaluating the results of panel drip tests. More particularly, a need exists in the field of panel drip tests for a method of quantitatively evaluating panel drip tests, for example by use of a mathematical algorithm. Additionally, a need exists for a method of quantitatively rating glass panels tested using drip tests to provide quantitative results that would allow the best solvent to be selected from a number of tested glass panels. Further, a need exists for an improved apparatus by which panel drip tests are conducted, recorded, and evaluated. A method and apparatus for evaluating glass quantitatively the ability of a solvent to clean a coating from a substrate using a panel drip test provided in accordance with the present invention fulfills the foregoing needs.